The present invention relates to measurement of the traveling speed of the surface of a phase contained in another phase. One typical measurement of this type is measurement of blood corpuscle sedimentation rate.
Three similar methods are presently being employed in laboratory work to measure, for example, the blood corpuscle sedimentation rate. The most popular method is the Westergren method, described in Leitfaden der Labormedizin [Guide to Laboratory Medicine] by Jg. Meyer-Bertenrath, published by Deutscher Arzteverlag (1975), in which a calibrated Westergren pipette is filled to the 200 mm mark with a citrated venous blood sample and is put into a vertical position, and the value of the plasma phase above the interface is measured in mm after 1 h and after 2 h. The drawback of this method is the very long time required for the measurement. Moreover, since the interfaces become diffuse, or indistinct, in the course of time, any reading has an inherent error of about 2 mm. Of this inherent error, 1 mm is a reading error and the rest is the result of errors in the initial fill level. Additionally, the precise moment of reading is often missed so that the correct measuring value may be lost.
Much less used is an automatic blood sedimentation rate measuring device, manufactured by the DEHAG company, which measures according to the above method and automatically takes a reading after 1 h and after 2 h, the reading being stored in a mechanical counter and digital output being possible. Here, too, the vessel must be filled precisely to a given mark since the measurement is based on use of this mark as the starting fill level. The measuring accuracy is rated at 0.4 mm, to which is added the filling error and the starting time selection error representing about 0.5 mm so that the total error here is about 0.9 mm. A drawback of this device is again the long time required for the measurement.
The so-called "oblique" test is the fastest method presently in use. It proceeds in a manner similar to the above method except that the pipette is arranged at an angle of 45.degree. and a useable reading can already be taken after 1/2 h. However, the reading accuracy is worsened to about 2 to 5 mm, depending on the width of the transition region between the phases. Moreover, in this method errors may occur due to failure to make a reading at precisely the correct instant, resulting in the loss of a useable measurement. In all cases, the patient and the physician are forced to wait too long to obtain the final result which is then given only as a qualitative indication.